geology lab 7 humid and arid landscapes

trellis drainage pattern

abundance of right angle intersection with strong structural control, usually found in strike valleys

landforms susceptible to wind deflation

alluvial fans, playas and pediments

where are angular landforms more common

arid lands where physical weathering gains relative importance

what is land like in dry environments

bare rock surfaces common because of absence of soil and vegetation mantle

types of eolian dune

blowout, migrating blowout, linear dunes, transverse ridges, barchanoid ridges, barchans, star dunes

parabolic dune

blowouts elongated through time with their sediment deposited on downwind side

blowout or deflation hollow

closed depression scooped out by prolonged deflation

desert pavement

coarse lag deposit of gravelly material remaining after deflation occurs

point bar deposit

deposition on inside on meander bend resulting in sand/gravel bar

floodplain

flattish area adjacent to channel of lateral cutting stream regularly flooded

intermittent streams

flow only seasonally

oxbow lake

formed from cutoffs

radial drainage pattern

formed when streams flow radially outward from central peak

drainage pattern

geometric pattern stream and its tributaries form

youthful arid climate

high relief, fault scarps, extensive alluvial fans, interior drainage, intermittent streams, angular topography, playa

braided channel patterns

high width to depth ratio because too much solid/coarse load carried by water

mature humid climate

high yet decreasing relief, broader valleys, no remnants, floodplain development, gentle valley sides, main streams by base level

youthful humid climate

increasing relief, v shaped valleys, steep stream gradients, lack of floodplains, remnants of initial uplifted surface, rapid downcutting

playa

intermittent lake bed

streams in arid regions

intermittent streams disappearing only few miles from sources

environmental factors promoting wind erosion in arid regions

lack of soil moisture, incomplete vegetation cover, periodic strong winds, availability of loose surficial deposits

old age humid climate

low relief, broad floodplains, gentle round interfluves, monadnocks, streams approaching base level with low gradients

old age arid climate

low relief, extensive pediments and bajadas, thickened playa deposits, scattered inselbergs

how does braided channel pattern get its appearance

mid channel bars protruding above water level during periods of normal stream flow

mature arid climate

moderate relief, steep mount front, parallel retreat, pediments, bajadas, rising base level, eolian dunes, angular topography

pluvial climates

more humid climates from past producing many features such as wave cut cliffs and beaches formed around pluvial lakes existing only during these wetter periods

dendritic drainage pattern

most common pattern which forms branch like pattern, smaller streams join larger ones at acute angle

meandering channel patterns

narrow single sinuous channel; high channel velocities at outside of bends create periodic erosion; low velocities at inside create deposition

wind, glaciers, waves, currents

other erosional agents

backswamps

oxbow lakes filled with silt, sand, clay, vegetation

interruptions to erosion cycle

periodic effects of climatic change, tectonic activity (folding and faulting), glaciation, changes in sea level and volcanism

wind deflation

process selectively removing finer grain from surface

the base level in humid climates

sea level because most rivers run to sea

what is land like in humid environments

soil and vegetation cover concealing bedrock outcrops

cutoff

stream meandering wildly and looping back on itself

rejuvenation

stream's energy is renewed and cycle of erosion not completed

where does increase in discharge happen

streams in humid regions as they are traced downwards

natural levee

successive deposits built by deposition of alluvium next to main stream channel

meander scroll

successive point bar deposits form series of arcuate deposits

why do rounded landforms dominate humid climates

the abundance of water and dominance of chemical over physical weathering

remaining 25% of continents on earth

the amount of earth arid and semi arid climates cover

75% of continents on earth

the amount of earth humid climates cover

streams

the dominant erosional agent in humid and arid climates

the base level in arid climates

the level of the playa because of interior drainage

base level

the lowest vertical limit to which streams can erode

the controls of climate contrasts

the way streams modify landscape and the importance of other agents in sculpting land

what kind of streams have distinctive channel pattern

those flowing across alluvial floodplain

stream terraces and entrenched meanders

two common landforms thought to reflect rejuvenation

discharge

volume of water flowage

lateral cutting

when streams approach local base level or erosion and decrease downcutting

alluvial fans

widespread stream deposits at base of many western mountains due to intermittent streams in arid regions

eolian features

wind produced and more obvious in arid lands, especially where eolian dunes are widespread

how does humid cycle of erosion begin

with low relief as an entire block of crustal material is uplifted

how does arid cycle of erosion begin

with maximum relief due to block faulting